google-plus, twitter, and now even yahoo! with its promising photo app flickr are each trying to slow facebook's momentum. >> mark zuckerberg doesn't lay awake thinking about google-plus. he lays awake thinking about the next instagram. >> reporter: that was just prior to the ipo and partially before zuckerberg took rival instagram off the table, buying it for $1 billion. questioned at the time, most valley insiders see the large price tag as a worthy investment. >> i think it was definitely a smart acquisition. the challenge is, in some sense, they were playing with funny money. the value that the market was giving them for their company was so high that do you give up 1% of your company to a small company that has the chance to take over your entire user base? it's an insurance policy, and the it a small price. >> reporter: the jury is still out on facebook's other moves, such as gifts, the company's entry into e-commerce, as well as smart phone advertising, increasingly seen as the key to facebook's growth. >> on mobile, t